This invention relates to a method and apparatus for folding a continuously fed web in two. Such a method and apparatus are adapted to be used for continuous production of disposable pull-on wearing articles such as disposable pull-on diapers.
Japanese Unexamined Patent Application Publication No. 1977-29339 (Citation 1) discloses the invention relating to “Method and apparatus for folding and cutting continuous web”. The invention disclosed in this document allows a continuously fed web comprising a series of diapers successively connected one to another and including elastic strands stretched in parallel to a direction in which the web travels to be folded along a longitudinal direction from its transversely flattened state so that the web may present a C-shaped cross-section. For such folding, a board folder of well known art is used.
U.S. Pat. No. 4,650,530 (Citation 2) discloses the invention relating to a method and apparatus for folding, bonding and cutting a continuously fed web. According to the disclosure of this document, a projection radially extending from a periphery of a rotary disc come in contact with a transversely middle region of the web running in a machine direction and serve as point of support for the web which is, in turn, folded in two lying on both sides of the rotary disc, respectively. The apparatus disclosed in this document allows the pants-type wearing article to be continuously manufactured.
Japanese Unexamined Patent Application Publication No. 2003-38566 (Citation 3) discloses a method and apparatus for making disposable wearing articles. Such a method and apparatus use a folder adapted to fold a web in two so that transversely opposite side edges of the web may be placed upon each other, an adjuster adapted to position-adjust the web, a detector adapted to detect an actual line along which the web is being folded, and a controller adapted to control the adjuster on the basis of information supplied from the detector. The adjuster includes a web guider which includes, in turn, guide rolls extending across the web before folded in two. The guide rolls are in contact with the web in the vicinity of its transversely opposite side edges and controlled by the controller to swing so that a cross angle of the web with respect to a direction in which the web runs may be changed. Depending on the cross angle, the guide rolls adjust a tension in the web's running direction exerted on the web in the vicinity of its transversely opposite side edges so that the web may run along a predetermined path.
With the method and apparatus disclosed in Citation 1, the web is folded along edges of the board folder opposed to each other when the web is folded in the transverse direction so as to present the C-shaped cross-section. However, there is provided none of particular means serving to align the web and the board folder with each other and therefore the web can not present the expected C-shaped cross-section if the transversely middle region of the web is out of alignment with the transversely middle region of the board folder.
The method and apparatus disclosed in Citation 2 also have none of particular means serving to align the projection of the disc with the transversely middle region of the web. If the web is out of alignment with the disc in the transverse direction, the pants-type wearing article obtained will have respective ends of the front and rear waist regions being out of mutual alignment in a direction of the article's height.
The method and apparatus disclosed in Citation 3 use the guide rolls extending across the web to guide the web so that, as one of the side edges of the web is position-changed, the other side edge also is correspondingly position-changed. While these method and apparatus are effective so far as these method and apparatus are used for a non-stretchable web, it is difficult to expect the same effect when these method and apparatus are used for elastically or inelastically stretchable web. This is because the other side edge of the web is not necessarily position-changed in accurate correspondence with the position-change of the one side edge of the web. Furthermore, while it is possible for these method and apparatus to position-change the side edges of the web before the web is folded in two, it is impossible to position-change the side edges of the web once the web has begun to be folded. In addition, if a distance from the point at which the web has begun to be folded to the point at which the web is completely folded is relatively long, a distance of a downstream region from the guide rolls will be correspondingly long. Consequently, the function of the guide rolls to position-adjustment of the web is hardly effective upon the web which have already been folded. In other words, it is difficult for these guide rolls to maintain the exact relative positions of the transversely opposite side edges of the web which has been folded in two.